Slightly improved register assignment for %_IsObject on IA32 and ARM.

src/arm/lithium-arm.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1080 matching lines @@
     return new LHasCachedArrayIndexAndBranch(
         UseRegisterAtStart(compare->value()));
   } else if (v->IsIsNull()) {
     HIsNull* compare = HIsNull::cast(v);
     ASSERT(compare->value()->representation().IsTagged());
     return new LIsNullAndBranch(UseRegisterAtStart(compare->value()));
   } else if (v->IsIsObject()) {
     HIsObject* compare = HIsObject::cast(v);
     ASSERT(compare->value()->representation().IsTagged());
     LOperand* temp = TempRegister();
-    return new LIsObjectAndBranch(UseRegister(compare->value()), temp);
+    return new LIsObjectAndBranch(UseRegisterAtStart(compare->value()), temp);
   } else if (v->IsCompareObjectEq()) {
     HCompareObjectEq* compare = HCompareObjectEq::cast(v);
     return new LCmpObjectEqAndBranch(UseRegisterAtStart(compare->left()),
                                      UseRegisterAtStart(compare->right()));
   } else if (v->IsCompareConstantEq()) {
     HCompareConstantEq* compare = HCompareConstantEq::cast(v);
     return new LCmpConstantEqAndBranch(UseRegisterAtStart(compare->value()));
   } else if (v->IsTypeofIs()) {
     HTypeofIs* typeof_is = HTypeofIs::cast(v);
     return new LTypeofIsAndBranch(UseTempRegister(typeof_is->value()));
@@ skipping 1122 matching lines @@
 
 LInstruction* LChunkBuilder::DoIn(HIn* instr) {
   LOperand* key = UseRegisterAtStart(instr->key());
   LOperand* object = UseRegisterAtStart(instr->object());
   LIn* result = new LIn(key, object);
   return MarkAsCall(DefineFixed(result, r0), instr);
 }
 
 
 } }  // namespace v8::internal